St. John's Wort and Plavix May Be Risky Combo
Herb Could Increase Bleeding Risk of a Blood-Thinning Drug, Researchers Say
March 8, 2005 - St. John's wort, used by many for depression, increases the effect - and the
bleeding risk - of Plavix, a widely used blood thinner.
The finding comes from a small study of just six people. To confirm the
interaction, larger studies are needed. But the finding supports what doctors
have been saying for years: Herbal remedies are strong medicine. They can
interact with prescription drugs in unexpected ways, says researcher Wei C.
Lau, MD, director of adult cardiac anesthesia at the University of Michigan
"Drugs can interact with drugs, and drugs can interact with herbals -
and the result in either case can be dangerous," Lau says in a news
Plavix is a drug given to prevent blood clots. It's usually given to people
who have had a heart attack or a stroke
caused by a blood clot. It helps reduce the risk of future heart attacks or
strokes by preventing blood clots. However, not everyone responds to the
Lau's team studied six healthy volunteers. In earlier studies, these
volunteers were found to be resistant to the blood-thinning effects of Plavix.
The researchers say this is likely due to underactivity of a liver enzyme that
normally activates Plavix.
St. John's wort increases the activity of this enzyme. So researchers put
these patients on Plavix and St. John's wort.
The researchers say that by taking the herb, Plavix is activated in the
body, allowing it to have a stronger blood-thinning effect.
Sure enough, the herb greatly increased Plavix's effect.
No one should take St. John's wort to increase the effects of Plavix. This
study shows that the two together could cause dangerous blood thinning that
could lead to severe bleeding - even in the brain.
But if this finding is confirmed in larger studies, it may help patients who
appear to be resistant to the effects of Plavix get more out of the drug.
Meanwhile, the study serves as a reminder to tell your doctor about all the
herbal remedies you may be taking.
Lau reported the study findings in a poster presentation at this week's
Annual Scientific Sessions of the American College of Cardiology in Orlando,